1. Field of the Invention
The present invention relates to a method for generating a gamma voltage, a driving circuit for performing the method and a display device having the driving circuit. More particularly, the present invention relates a method for generating a gamma voltage, a driving circuit for performing the method capable of decreasing manufacturing costs thereof, and a display device having the driving circuit.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) panel includes a gate line, a source line, a switching element, and a pixel electrode. The gate line and the source line are formed from different metal layers. The switching element is electrically connected to the gate line and the source line. The pixel electrode is formed from a transparent conductive material to be electrically connected to the switching element. The LCD panel includes a common electrode facing the pixel electrode. The pixel electrode, the common electrode and a liquid crystal layer interposed between the pixel electrode and the common electrode define a liquid crystal capacitor. A storage common electrode formed from the gate metal layer and the pixel electrode define a storage capacitor.
The LCD panel includes a liquid crystal capacitor, a storage capacitor and a parasitic capacitor between a gate electrode and a source electrode of the switching element. The liquid crystal capacitor, the storage capacitor and the parasitic capacitors may define a kickback voltage ‘Vck’, which is defined by the following Equation 1.
                    Vck        =                              Cgs                          Clc              +              Cst              +              Cgs                                ⁢                      (                          Von              -              Voff                        )                                              Equation        ⁢                                  ⁢        1            wherein ‘Vck’ represents a kickback voltage, ‘Clc’ represents the liquid crystal capacitance of the liquid crystal capacitor, ‘Cst’ represents the storage capacitance of the storage capacitor, ‘Cgs’ represents the parasitic capacitance between a gate electrode and a source electrode, ‘Von’ represents a gate-on voltage, and ‘Voff’ represents a gate-off voltage. The liquid crystal capacitance Clc is defined as ∈A/d, wherein ‘∈’ represents the dielectric constant of the liquid crystal, ‘A’ represents the size of a pixel electrode, and ‘d’ represents the cell gap of the liquid crystal layer.
Referring to Equation 1, the liquid crystal capacitance Clc has a different value according to the liquid crystal phase, so that the kickback voltage Vck has a different value for every gradation of liquid crystal phase. For example, when the liquid crystal molecules are in a twisted nematic (TN) mode and a normally white mode, the kickback voltages of each of 64 gradations are defined by the following Equation 2.Vck(0Gray)<Vck(1Gray)<, . . . ,<Vck(32Gray)<, . . . ,<Vck(62Gray)<Vck(63Gray)  Equation 2
As shown in Equation 2, due to the difference of kickback voltages for each gradation, when a gamma reference voltage is set by a unique kickback voltage, flickering, afterimages, etc., may be generated.